Controllable synthesis of defect-enriched MoO3 for enhanced H2S sensing through hydrothermal methods: Experiments and DFT calculations

To improve the sensitivity of MoO3 sensors for hydrogen sulfide (H2S), two-dimensional MoO3 nanoflakes with enriched oxygen vacancies were synthesized by hydrothermal method. The relationship between the oxygen vacancies concentration, the hydrothermal method temperature, and the solution concentration (ethanol) was studied. The morphology, structure, and gas-sensing performance of MoO3 were measured and compared. Through qualitative analysis of lattice movement characterized by XRD, as well as the Mo5+ and adsorbed oxygen content determined by XPS, it was found that the synthesized material MoO3−x-13021 had the highest concentration of oxygen vacancies. The synthesized material coded as MoO3−x-13021 with the highest oxygen vacancy concentration showed enhanced H2S-sensing properties compared to defect-free MoO3 sensors. The response value reached 282.6 at 15 ppm. The optimum operating temperature was 140 ℃. Density Functional Theory (DFT) calculations were performed to establish the H2S sensitization mechanism model. Adsorption energies, bond lengths, charge transfer, and density of states (DOS) of H2S adsorbed on stoichiometric and reduced MoO3(010) surfaces were calculated and compared. The increase of oxygen vacancies on reduced MoO3 leads to the movement of the conduction band, which reduces the band gap of MoO3. This promotes the charge transfer between the gas molecules and MoO3, enhancing the response.